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The corundum stones come in all colors.

Colorful corundum gems

Corundum are sapphire and rubies combined which make it understandable that the are physically the same minerals except the colors are different.

Considering corundum gems in the precious stone pantheon this is all the more amazing, for together the ruby and the sapphire account for over 50% of the world trade in colored gemstones. Certainly, it is not for lack of interest. The ruby and sapphire have long been considered among the most highly sought after and most precious of gems. No, we must look elsewhere for answers, if indeed they can be found at all. Corundum, unlike the diamond, the pearl, and others, is, by and large, an Asian gem.

Considering corundum gems in the precious stone pantheon this is all the more amazing, for together the ruby and the sapphire account for over 50% of the world trade in colored gemstones. Certainly, it is not for lack of interest. The ruby and sapphire have long been considered among the most highly sought after and most precious of gems. No, we must look elsewhere for answers, if indeed they can be found at all. Corundum, unlike the diamond, the pearl, and others, is, by and large, an Asian gem.

Considering corundum gems in the precious stone pantheon this is all the more amazing, for together the ruby and the sapphire account for over 50% of the world trade in colored gemstones. Certainly, it is not for lack of interest. The ruby and sapphire have long been considered among the most highly sought after and most precious of gems. No, we must look elsewhere for answers, if indeed they can be found at all. Corundum, unlike the diamond, the pearl, and others, is, by and large, an Asian gem.

From the fabled Mogok Stone Tract in the ASEAN heavyweight Myanmar / Burma to the gem gravels of Sri Lanka, we find the historical occurrences of rubies and sapphires largely restricted to Asia — lands as different from the West as night is from the day. Rudyard Kipling summed up these differences best when he made the (oft-quoted) remark: 'East is East and West is West and never the twain shall meet.' Travelers from the West have been venturing to the Orient continuously since Roman times and before; much of the region was later colonized by the European

The colors of Corundum

When the diverse range of colors to be found among the corundum gems is considered, it is indeed remarkable, and surely must have seemed so to the ancients, that they are all one and the same mineral. In fact, no other mineral except tourmaline displays such a wide range of colors. From pigeons blood red to cornflower blue, almost the only color not found is a true emerald green, although a less intense olive green is often encountered.

But who knows, possibly someday a lucky miner will unearth this 'missing link' too! The reason for the broad range of colors in corundum concerns its chemistry. Corundum is composed of aluminum oxide (Al203) which, in its pure state, is completely colorless. However, pure corundum is rarely encountered in nature. Instead, a small number of impurity metals may individually or together replace aluminum atoms in the crystal structure, thus imparting color.

Beryl and tourmaline are also colored by impurities; a state termed `all chromaticity'. In contrast, `idiochromatic' minerals are those that are colored by essential elements in their chemical make-up, and so occur only in one basic color.

Turquoise is an example of the latter, always being found in the blue-green hue for which it is famous. In synthetic corundum, a number of different dopants have been found to be useful in producing different colors, but with natural corundum, the number is rather limited. There is still much to be found put regarding the true causes of color in corundum, but in many cases, a fairly clear picture has emerged.

Most varieties of corundum appear to be colored by a peculiar group of elements termed 'transition elements', which are responsible for the hues of a number of different creations of nature besides minerals. These elements are in the center of the periodic table and are peculiar because their electron structure contains inner unpaired 'free' electrons which can be excited or elevated, to higher energy levels by absorbing.

For a reasonable start we better first examine the mechanism of color itself. White light, or sunlight, is made up of a balanced mixture of all the different spectral colors — violet, indigo, blue, green, yellow, orange and red. An object or material does not really possess color itself; instead, color is merely a perception based on a complex interaction between the light source, the object, and our eyes. White and black are not spoken of as colors in the true sense of the word.

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What is color?

Instead, the sensation of white is created by equal amounts of all the wavelengths of coloured light, from 400 to 700 nm, striking the eye. Black is simply a lack of any visible light reaching the eye. An object appears colored because of its selective absorption of visible light. This is the manner by which it absorbs some wavelengths, or colors, while freely transmitting '.or reflecting others. The actual colour we see depends on our eyes' interaction with the wavelengths which strike the eye and is often the complementary colour of the light absorbed. In the simplest terms, grass appears green because, when white light falls upon it, all colours are absorbed except green.

Absorbed, a green sensation is produced when they strike the eye together. If the grass was illuminated with a red light, it would appear black because the red lights absorbed by it; thus, no visible light reaches the eye. To someone who is blind, the grass would appear red when illuminated by white light because of a lad of green-sensitive optical components, or cones, in the eye. From these examples we can see that the grass appears green not just because of the way it absorbs light, but also because of the physiology of our eyes and, of equal importance, the spectral composition of the light source by which it is illuminated. With this in mind we will now look at specific situations in corundum.

The colour of ruby can be attributed to electron transitions which substitutes Chromium for aluminum in amounts approximating 1%. That chromium, able to absorb visible light concerns its outer electron suborbital, which lie close enough together that visible light is absorbed by boosting unpaired electrons M3 higher excited state. Electromagnetic radiation is commonly specified by referring to its wavelength with different types of radiation having different wavelengths, ranging from very long radio waves to the extremely short x-rays and y-rays. Another way, specifying the type of radiation is by its energy, usually given in electron volts . The shorter the wavelength, the more powerful its energy. In order for a chromium atom to absorb visible light, its electron energy must lie just the right distance apart.

Transparent colored varieties of corundum — the bright-red rubies and the blue sapphires with their color resembling cornflowers, the rank among the most precious and prized gemstones and their market price often exceeds even that of diamonds. Corundum is one of the gemstones that Nye been used by man for longest In classical Greek times a corundum locality was known on the island of Naxos in the Aegean Sea.

The oldest written records of ruby mining, at Mogok in Upper Burma, date from the sixth century as The name ruby is derived from the Latin rubeus (= red); the origin of sapphire's name remains a mystery. Corundum forms hexahedral, short-to-long columnar crystals of a spindle or barrel-shaped habit (Fig.). Rarer are the low tabular crystals with a large base. Alluvial deposits often contain corundum in the form of rounded grains or pebbles. With its hardness of 9, corundum is the hardest mineral after diamond.

However, the hardness depends on the crystallographic direction: the base of the crystal is harder than the faces of the prismatic zone. Corundum has no natural cleavage, but large crystals may part parallel to the base (so-called false cleavage). It has a high, vitreous luster, which may be of a pearly character on the bases. It usually withstands heating quite well but when jewels decorated with corundum are repaired, they must be heated and cooled slowly. Some sapphires will change hue if annealed. Corundum has a worldwide occurrence. It crystallizes in granites, in nephelinic syenites, crystalline schists, gneisses, contact-metamorphosed lime I stones and dolomites. Because corundum is mechanically and chemically resistant it often occurs secondarily in alluvia. The relatively high specific gravity of the stones permits easy placer ruining (panning). Depending on their origin, natural corundum contains various inclusions and in-growths of small crystals of other minerals, as well as gaseous and liquid inclusions. These foreign inclusions are usually typical for certain localities and are a better guide to the locality and origin of stones than are hues.

A microscopic observation of foreign inclusions is also a useful method for distinguishing natural stones from synthetic ones. Corundum is found in many color hues. Some crystals may even be multicolored and show color zoning. The most transparent colorless corundum variety is called leucosapphire. Unlike the synthetic stones that are always perfectly colorless, natural leucosapphires have a slight tinge, although leucosapphires are much rarer in nature than rubies or sapphires, they are less valued for jewelry.